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<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
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    <title>Document</title>
    <style>
        .a {
            width: 200px;
            height: 200px;
            /* 边框是由 边框粗细+边框颜色+边框样式组成的   边框也会把盒子撑大 */
            /* border: 2px red solid;  简写，不分先后顺序 */

            /* border-width: 2px;   边框的粗细 */
            /* border-color: red;   边框的颜色 */

            /* 实线solid   虚线dashed   点线dotted */
            /* border-style: solid; 边框的样式 */

            /* border: red 2px solid; */

            /* border-bottom: 3px solid #000; */

            background-color: #ff0;
            border: 10px solid #000;

            /* 
                盒子模型：外边距+边框+内边距+内容 margin border padding 
                盒子模型是css布局的基石 
                盒子的实际宽度=外边距+边框+内边距+内容(width)
            */
        }

        h3 {
            line-height: 60px;
            border-bottom: 1px solid #000;
            margin-left: 20px;
        }
    </style>
</head>

<body>

    <div class="a"></div>


    <h3>产品中心</h3>

</body>

</html>